EVA represents one of the most important types of ethylene copolymers. EVA is used in wide range of applications, including packaging, hose and tubing, footwear, melt adhesives, cable and wire insulation, etc. In these applications, it is desirable for the EVA to have a high level of fire retardancy and excellent strength.
In the past, EVA has been combined with other materials to form EVA nanocomposites. EVA in the form of a silicate-containing nanocomposite has been preferred to impart increased strength and fire retardancy compared to neat EVA. Most EVA/silicate nanocomposites reported previous to the invention herein were prepared by melt intercalation of organically modified silicate with EVA or solution intercalation of organically modified silicate into EVA. However, the organic modifier of these EVA nanocomposites is subject to decomposition and/or volatilization, which may then lead to the collapse of the interlayer of the silicate and reduced mechanical stability of the nanocomposite.
Additionally, while the addition of silicate to EVA via, for example, intercalation, tends to improve the mechanical properties of the EVA nanocomposite, such methods also impair the toughness of the EVA nanocomposite.
Furthermore, when silicate is intercalated in a polymer as described in previous methods, the advantages of introducing the silicate into the polymer may be lost upon further processing of the composite material. Silicate is initially present as attached spaced plates or layers of silicate. During intercalation, polymer is inserted in the spaces or galleries of the silicate and the overall spaced plate arrangement of the silicate is preserved. The resultant structure is therefore a silicate structure with polymer in interspaces of a coherent silicate structure. Upon further processing of the composite material, such as melt processing, the polymer may migrate out of the interspaces of the silicate, thereby diminishing the benefit of adding silicate in the first place.
Accordingly, it is desirable to provide a method of making an EVA nanocomposite that improves the mechanical properties of the EVA nanocomposite without impairing toughness and to provide an EVA nanocomposite with substantially exfoliated silicate in a polymer phase, which can in turn be heat processed without losing exfoliation.